This invention concerns a directed-effect munition designed to be launched, by means of a vector, above an area containing a target, wherein the munition includes a warhead having a shaped charge and a detection device that actuates a detonation device.
The invention concerns in particular a submunition designed to be expelled by a mine or a vector, the submunition being in turn launched by an aircraft or an artillery piece, such that the submunition is given a displacement velocity v along a substantially vertical axis V, and a rotation velocity r substantially about the same axis.
A weapon system of this kind is described U.S. Pat. No. 4,858,532 to Persson et al. The axis of the detection device is tilted approximately 30.degree. with respect to the rotation axis of the submunition so that during its descending movement, the surface region covered by the detector device at a given moment moves in spiral fashion over the detection area, thus increasing the probability that the target will be detected.
When the target is detected, a signal triggers the shaped charge, which acts vertically downward while the submunition is in a substantially vertical descending portion of its trajectory. It is evident that a warhead of this type could just as easily operate in an ascending trajectory, as in the case of the first part of the trajectory of a submunition launched by a land mine.
Such a system has the advantage that targets can be engaged remotely, with no need for guidance, and with the use of a simple detection scheme.
However, this structure has considerable drawbacks resulting firstly from inaccurate detection, since the appearance of a detection signal means only that at least a part of the target is within the detection zone, and resulting secondly from well-known error sources associated with the velocity components v and r of the submunition.
To clarify the drawbacks of the prior method, the implementation principles of the method will be described below with reference to FIGS. 1 to 5 of the attached drawings.
FIGS. 1 to 5, which refer to a conventional submunition, illustrate a submunition 1 including a shaped charge 2 that moves with a displacement velocity v along a substantially vertical axis V, and with a rotation velocity r about an axis substantially identical to V, in the vicinity of a plane 3 containing a target 5, such as a land vehicle.
Shaped charge 2 has rotational symmetry about an axis D that forms an angle t with axis V. A detector 7, with a detection axis d substantially parallel to axis D, can act on an igniter 8 placed behind shaped charge 2. Detection axis d rotates about axis V, scanning a surface area whose intersection with plane 3 containing target 5 forms a spiral 9. Detection is effective within a solid angle with axis d, impinging on plane 3 over a surface area 4. FIG. 1 shows a spiral 10, which to some extent encompasses spiral 9 and corresponds to the envelope in plane 3 of the outline of instantaneous detection surface area 4.
FIG. 3 diagrams the impact point deviation resulting solely from rotation of the charge. The plane of FIG. 3 is parallel to the target plane, which is assumed to be horizontal. Circle C with center 0 is the location of the detected points (intersection between detection axis d and the ground), and circle C' is the location of the impact points on the ground. The target, located at point M, is detected at time t.sub.0 and firing is triggered at time t.sub.1 (t.sub.1 -t.sub.0 =a, corresponding to the calculation time).
If r is the rotational velocity of the charge, and n is the distance between the center of gravity of the casing of the explosively formed penetrator, and rotation axis V, angle s1 is equal to r.a, and is induced by rotation of the charge during the calculation time. It causes point M to correspond to a point M" on circle C.
Angle s2 is equal to arctan (n.r/V.sub.pen.sin t), V.sub.pen being the velocity (assumed to be constant) of the penetrator after firing. This angle is induced by the velocity n.r impressed by the charge on the penetrator velocity. It causes point M" to correspond to a point M' on circle C'. The total error is equal to MM'.
The angular error resulting from s=s1+s2 is constant over time, and always acts in the same direction. Thus, the impact point is always ahead of the detected point in the direction of rotation. It is thus possible, with a fixed shift in the detection axis with respect to the axis of the charge, to compensate for this error and reduce the total error to merely the deviation M.sub.1 M' (M.sub.1 being the point on circle C offset from point M by an angle s).
The error M.sub.1 M', however, still remains to be corrected.
If angle s is constant, deviation compensation could be implemented by shifting detection axis d forward by an identical amount, but error M.sub.1 M' would still need to be compensated for.
With regard to the impact deviation due to the substantially vertical displacement velocity v of the charge, a listing will first be given of the orders of magnitude ordinarily encountered with this type of submunition:
v=50 m/s
Velocity of the penetrator generated by the charge: V.sub.efp =2000 m/s
t=30.degree.
Target distance=100 m
Time from detection to charge triggering: a=0.5 ms
Impact point deviation: 1.4 m.
This error also depends on the direction of movement of the submunition. During ascent, the impact point is displaced toward the outside of the spiral; during descent, the impact point is displaced toward the inside of the spiral.
In FIG. 4, the impact deviation has been diagrammed for the case of an ascending charge trajectory; and axis Z represents the vertical axis and axis R represents the axis of the radial distances of the impact point, designated here by P.
For a time a, point Q symbolizing the position of the charge is displaced a distance a.v and moves to Q1. By systematically shifting the position of the detector, an initial correction can be applied by moving from P to P.sub.1, line Q.sub.1 P.sub.1 being parallel to QP; but an error P.sub.1 P' would remain.
However, this kind of correction would be disadvantageous for the descent phase, as shown in FIG. 5, since it would correspondingly increase the deviation PP".